Fluid regulators (flow-rate control valves) for controlling the flow rate of various types of fluid, such as chemicals, have been widely used. According to the general structure of such a fluid regulator, a diaphragm receives pressure fluctuations at the primary side (upstream side), and a valve that operates together with the diaphragm adjusts a valve opening in a fluid flow path to control the flow rate.
Recently, for example, in chemical feeding in a wafer cleaning line of a semiconductor manufacturing apparatus, there have been demands for highly accurate flow-rate control that can respond not only to pressure fluctuations at the primary side but also to pressure fluctuations at the secondary side (downstream side). Examples of the pressure fluctuations at the secondary side include the effect of back pressure generated by, for example, a confluence of a plurality of flow paths or pressure fluctuations at the primary side, and load fluctuations caused by, for example, a change in the fluid viscosity due to temperature changes.
In view of this background, the following flow-rate control valve has been proposed as a flow-rate control valve that can also respond to the above-described pressure fluctuations at the secondary side. In this flow-rate control valve, a fluid at the secondary side is introduced into a differential pressure chamber in which diaphragms having different effective areas are provided at the upper side and the lower side to control the flow rate. In this case, the upper and lower diaphragms receive the same pressure fluctuation in the differential pressure chamber. Accordingly, since a working force for operating a valve is generated in accordance with the difference in the area of the diaphragms, the flow rate is controlled depending on the change in a valve opening (see for example Patent Document 1).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. Hei-11-85287